1. Field of the Invention
The present invention generally relates to an image data recording system for receiving an optical image incident upon an image recording system through a lens, for converting the received optical image into electronic image data, and for storing the electronic image data therein. More specifically, the present invention is directed to an image data recording system utilizing memory cards to store the electronic image data.
2. Description of the Related Art
As an image data recording system, a so-called "electronic still camera" has been practically marketed. In the commercially available electronic still cameras, still images are optically and electrically processed to be stored in a recording medium, for instance, a magnetic disk.
More specifically, in the conventional electronic still camera, a semiconductor imaging element, e.g., a charge-coupled device (referred to as a "CCD") is employed to optically receive a still image and convert it into a corresponding electronic image signal. After the electronic image signal is processed to have a signal format suitable for a television signal, the processed image signal is modulated into an FM (frequency modulation) image signal. Then, the FM image signal is recorded onto a magnetic disk in an analog signal form. If such an electronic still camera records the FM image signals with a field recording format, 50 still pictures or complete images can be recorded on a magnetic disk.
In such a conventional magnetic disk type electronic still camera, miniaturization of the electronic still camera meets with practical difficulties, because there is a size limitation to manufacture of a compact driving mechanism for driving the magnetic disk.
Accordingly, to solve these difficulties of the conventional magnetic disk type electronic still camera, another type of electronic still camera employing a built-in semiconductor memory (referred to as a "RAM") has been recently developed, in which an analog still image signal is processed to obtain a digital still image signal. The digital still image signal, or digital image data is stored in the built-in semiconductor memory (RAM).
However, the semiconductor memory type electronic still camera has another drawback. In general, when a single still image is stored into a semiconductor memory, a memory capacity of more than 2 M bits (mega bits) is required for each still image. Therefore, to store 50 still pictures (or images) in such a semiconductor memory type still camera, which is similarly performed in the magnetic disk type still camera, a semiconductor memory having a memory capacity of more than 100 M bits is required. However, a semiconductor memory type still camera having such an extremely high memory capacity is not practically available.